For flameless heating of its contents, a package which includes a flameless heater, and an improved flameless heater for the package.
Packages that contain a product, often a food product, are known which also include a flameless heater to heat the product on demand. Classical examples are provided to the military as Meals Ready To Eat (xe2x80x9cMRExe2x80x9d). In addition to the military, there are many other demands, such as emergency rations for shelters, for the sportsman in the field, and for heating of non-food products.
As might be expected, because of necessary extended shelf life and extreme exposure conditions, military standards are often more stringent than are necessary for less critical applications. When the products are intended for usage in man-sensitive circumstances, there is no realistic limit on the cost of such items. However, there are many uses for self-heating products where the shelf life is shorter, or where a somewhat lesser occasional performance is acceptable, in which the costs involved in a military grade product would exclude it from the commercial market.
As with any packaged product, the cost of the packaging containing a consumable product is often a disproportionally large part of the total. When performance is absolutely necessary, as established by such standards as MIL-R-443983 for a flameless ration heater, fabrication processes and materials of construction will reasonably be expected to be high. For these high standards, the configuration and contents of a heater can be related to a particular product and can be manufactured with expensive and time-consuming procedures. No one objects to the cost of providing only the best for military rations in the field, for example. But a housewife can reasonably object to an unnecessarily high price when an occasional overheat or underheat of a cup of chocolate is the only adverse consequence of a less than optimal heater.
It is also a useful objective to enable a different total caloric delivery for different foods that would be sold in an identical package. For example, a stew would require more calories per unit volume than a souffle, both of which could fit in the same package. This invention enables the source of heat to be adjusted both as to the amount supplied and where it can, be positioned, all without significant adjustments to the packaging or to the heat sources themselves.
A well-known flameless heating package is shown in Fulcher and Huang U.S. Pat. No. 5,465,707, which is incorporated herein in its entirety for its showing of a structural package of the class to which this instant invention relates. The improvements of this invention relate to the heater and to a package containing the improved heater. The said patent may be referred to for its showing of the theory, operation, and details of materials of the package and of its heater constituents. A well-known construction for a flameless heater element is shown in Kuhn U.S. Pat. No. 4,522,190. Still another is shown in Lamensdorf patent U.S. Pat. No. 5,611,329. In the Kuhn patent, a flameless heater comprised of an exothermic supercorrosive alloy of magnesium and iron is sintered into large single shapes which generally conform to the container for the product. In the Lamensdorf patent, instead of being a large sintered body, the supercorrosive alloy is a fine powder contained loosely in a shaped container. The shaped container is adapted to hold portions of the powder in defined regions.
The Kuhn construction is expensive. Sintering requires considerable process time. In addition there are the costs of handling, processing, and making sintering molds and dies, all of which drive up the price of the product.
In the Lamensdorf device. The powder simply slumps to the lowest point in its pockets, resulting in an uneven distribution of heatxe2x80x94too hot in some areas and too cold in others, and in an uncertain rate of production of heat. This less effective performance is accompanied by the larger cost of the segmented packaging and of its assembly. Even less effective would be a loose amount of powder in a large flexible envelope.
It is an object of this invention to provide a package for products with a flameless heater nearly equal in performance to those which meet the high military standards, but at an importantly lesser cost of components and assembly.
It is another object of this invention to provide a flameless heater which can accommodate and effectively heat products of widely differing sizes, shapes and caloric requirements without resorting to the use of loose powders or requiring formation of a large specially shaped structure for the heater.
A flameless heater for a package of product according to this invention utilizes a composition which, when wetted with water, will have an exothermal effect. The presently preferred substance is an exothermic supercorrosive alloy of magnesium and iron that is passive and stable while dry. Other exothermal sources can be used, included sources that are not electrochemical, and other electrochemical systems than this one. Heats of solution or of hydration (from calcium oxide, for example), are non-electrochemical exothermal sources within the scope of the invention.
When wetted with water containing an electrolyte, the customary exothermal and gas generating reactions occur with the preferred embodiment, as with the other useful substances.
According to this invention the alloy is preferably placed in a flexible heater pouch, a portion of which is both water-permeable and gas-permeable. The heater and the product are contained in an impermeable and insulating outer enclosure. The container for the product, or the product itself, is in heat conductive relationship, usually contiguous, to the permeable pouch.
This pouch itself is optional. When the product container and the outer package are suitably proportioned, the tablets may be distributed, between them without the assistance of a pouch.
According to a feature of this invention, the exothermic material is contained in tablet form, preferably compressed or possibly sintered, in a shape such that in a flexible pouch they can be distributed over a desired area, with a desired density distribution.
According to a preferred but optional feature of the invention, the tablets are compressed into a rigid self-shape retaining structure.
The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, in which: